Normal cats are being compared with cats whose carotid bodies have been resected in respect to their ventilatory responses to hypoxia in groups maintained at either sea level or at simulated high altitude. The phenomena of ventilatory acclimatization, of hypoxic tachypnea, of "blunting", and of central re-organization to permit aortic body chemoreceptor control of breathing are all being studied. A comparative study of hypoxic controller "gain" is being studied to determine its relationship to resting oxygen uptake rate.